1. Field of the Invention
The present invention relates to a position indicator in the shape of a pen, for example, which is used in conjunction with a position detecting device, and particularly to a position indicator having a function of detecting pressure (pen pressure) applied to a tip portion (pen point) of a core body.
2. Description of the Related Art
A position input device has recently been used as an input device for a tablet type PC (personal computer) or the like. The position input device includes, for example, a position indicator formed in the form of a pen, and a position detecting device having an input surface, on which pointing operation and input of characters, figures, and the like are performed based on the use of the position indicator.
Conventionally, as a pen type position indicator of this kind, a position indicator for a position detecting device of an electromagnetic induction system is well known. The position indicator of the electromagnetic induction system has a resonance circuit formed by connecting a resonance capacitor to a coil wound around a ferrite core. The position indicator indicates a position on the position detecting device by transmitting a resonance signal generated by the resonance circuit to the position detecting device.
The pen type position indicator of this kind is also configured conventionally to have a function of detecting pressure (pen pressure) applied to a tip portion (pen point) of a core body and transmitting the pressure (pen pressure) to the position detecting device. To detect the pen pressure, known methods use a mechanism that changes the inductance of the coil forming the resonance circuit according to the pen pressure or a mechanism that changes the capacitance of the capacitor forming the resonance circuit according to the pen pressure. When either of the methods is used, a pen pressure detecting section is formed into a pen pressure detecting module as one functional unit.
FIGS. 19A and 19B show a conventional example of construction of a variable capacitance capacitor type pen pressure detecting module that changes the capacitance of a capacitor forming a resonance circuit of a position indicator according to pen pressure. The conventional example is described in Patent Document 1 (Japanese Patent Laid-Open No. 2011-186803).
FIG. 19A is a general perspective view of the variable capacitance capacitor forming the pen pressure detecting module. FIG. 19B is a sectional view taken along line Z-Z of FIG. 19A, and is a longitudinal sectional view of the variable capacitance capacitor.
The variable capacitance capacitor 100 in the example of FIGS. 19A and 19B changes in capacitance according to pressure (pen pressure) applied to a core body 101 (see alternate long and short dashed lines in FIG. 19B) of the position indicator. The position indicator detects the pen pressure applied to the core body 101 on the basis of the change in the capacitance of the variable capacitance capacitor, and transmits the detected pen pressure to a position detecting device.
As shown in FIG. 19A and FIG. 19B, the variable capacitance capacitor 100 includes a dielectric 103, a terminal member 104, a retaining member 105, a conductive member 106, and an elastic member 107 within a cylindrical holder 102 made of a resin, for example.
The dielectric 103 for example has substantially a disk shape. The dielectric 103 has a substantially circular first surface portion 103a and a substantially circular second surface portion 103b opposed to the first surface portion 103a so as to be substantially parallel to the first surface portion 103a. In the present example, the first surface portion 103a and the second surface portion 103b are both formed in a planar shape.
As shown in FIG. 19B, the dielectric 103 is mounted on a flange portion 102a of the holder 102 with the second surface portion 103b faced toward another end side in an axial direction of the holder 102 on which end side the core body 101 is present.
The terminal member 104 is formed of a conductive metal. The terminal member 104 has a flat portion 104a as an example of a surface portion engaged with the first surface portion 103a of the dielectric 103, two locking portions 104b and 104c formed so as to be continuous from the flat portion 104a, and a lead piece 104d similarly formed so as to be continuous from the flat portion 104a. 
The two locking portions 104b and 104c have substantially the shape of a letter J, and are provided so as to sandwich the flat portion 104a therebetween. The two locking portions 104b and 104c provide elasticity to the terminal member 104 so that the flat portion 104a of the terminal member 104 is always biased elastically in directions toward end portions of the locking portions 104b and 104c. The end portions of the locking portions 104b and 104c are provided with opening portions 104e and 104f having substantially a quadrangular shape, for example.
As shown in FIG. 19A and FIG. 19B, the terminal member 104 is fixed to the holder 102, with the opening portions 104e and 104f of the two locking portions 104b and 104c locked to locking tooth portions 102b and 102c of the holder 102.
At this time, because the terminal member 104 has the elasticity provided by the two locking portions 104b and 104c, the flat portion 104a abuts against the first surface portion 103a of the dielectric 103 in a state of being pressed against the first surface portion 103a. The flat portion 104a of the terminal member 104 has a surface shape (flat surface in the present example) corresponding to the surface shape of the first surface portion 103a of the dielectric 103. Thus, the flat portion 104a and the first surface portion 103a of the dielectric 103 abut against each other without any gap therebetween, and are securely connected electrically to each other.
The lead piece 104d of the terminal member 104 is connected to a contact portion of a printed board (not shown), disposed on an opposite side from the core body 101, by resistance welding or ultrasonic welding, for example. The terminal member 104 is thereby connected electrically to electronic parts on the printed board. The lead piece 104d of the terminal member 104 forms a first electrode of the variable capacitance capacitor 100.
The retaining member 105 has a base portion 105a having an outside diameter slightly smaller than the inside diameter of a hollow portion of the holder 102 and a substantially cylindrical fitting portion 105b. An engaging recessed portion 105c (see FIG. 19B) recessed in substantially a cylindrical shape is provided in the base portion 105a. An end portion in the axial direction of the core body 101 is press-fitted into the engaging recessed portion 105c, whereby the core body 101 is coupled to the retaining member 105.
In addition, the fitting portion 105b as a recessed portion for attaching the conductive member 106 is formed in the retaining member 105 so as to project to an opposite side from the core body 101 side of the base portion 105a. The conductive member 106 is fitted into the fitting portion 105b. 
As shown in FIG. 19B, the conductive member 106 is formed in the form of a shell, for example, and has a curved surface portion 106a at one end in the axial direction of the conductive member 106. A cylindrical portion 106b on another end side in the axial direction of the conductive member 106 is fitted into the fitting portion 105b of the retaining member 105. The diameter of the cylindrical portion 106b of the conductive member 106 is, for example, set somewhat larger than the inside diameter of the fitting portion 105b of the retaining member 105. The relation of a fit between the conductive member 106 and the fitting portion 105b of the retaining member 105 is thereby set as the relation of a frictional fit. As a result, the conductive member 106 is prevented from falling off the fitting portion 105b of the retaining member 105.
The conductive member 106 has conductivity, and is formed of an elastic member capable of elastic deformation. Such an elastic member includes for example a silicon conductive rubber, a pressure conductive rubber (PCR: Pressure sensitive Conductive Rubber), and the like. When such an elastic member is used as the conductive member 106, a contact area between the second surface portion 103b of the dielectric 103 and the curved surface portion 106a of the conductive member 106 is increased with an increase in pen pressure (pressure) applied to the core body 101.
The elastic member 107 is for example a coil spring having conductivity. The elastic member 107 has a winding portion 107a having elasticity, a terminal piece 107b at one end portion of the winding portion 107a, and a connecting portion 107c at another end portion of the winding portion 107a. 
As shown in FIG. 19B, the winding portion 107a of the elastic member 107 is disposed so as to cover the periphery of the conductive member 106 with the fitting portion 105b of the retaining member 105 interposed therebetween. At this time, the connecting portion 107c of the elastic member 107 is interposed between the retaining member 105 and the conductive member 106, and comes into contact with the conductive member 106. The elastic member 107 is thereby electrically connected to the conductive member 106.
In addition, as shown in FIG. 19A, when the elastic member 107 is housed in the holder 102, the terminal piece 107b of the elastic member 107 projects to one end side in the axial direction of the holder 102 through a through hole (not shown) provided in the holder 102. The terminal piece 107b is connected to a contact portion (not shown) of the printed board by soldering, resistance welding, or ultrasonic welding, for example. The terminal piece 107b of the elastic member 107 forms a second electrode of the variable capacitance capacitor 100.
Two engaging projecting portions 105d and 105e having a substantially triangular sectional shape are provided on two flat surface portions opposed to each other in side surface portions of the base portion 105a of the retaining member 105. Engaging holes 102d and 102e with which the engaging projecting portions 105d and 105e of the retaining member 105 are engaged are formed in the holder 102.
In a state in which the conductive member 106 is fitted in the fitting portion 105b, and the elastic member 107 is disposed around the periphery of the conductive member 106 and electrically coupled to the conductive member 106, the retaining member 105 is press-fitted into the holder 102 so that the two engaging projecting portions 105d and 105e are engaged with the two engaging holes 102d and 102e provided in the holder 102. Then, the elastic member 107 is retained between the flange portion 102a of the holder 102 and the base portion 105a, and the retaining member 105 is retained in the holder 102 in a state of being movable along the axial direction of the holder 102 by the length of the engaging holes 102d and 102e in the axial direction of the holder 102.
At this time, as shown in FIG. 19B, the curved surface portion 106a formed on one end side in the axial direction of the conductive member 106 is disposed so as to be opposed to the second surface portion 103b of the dielectric 103, and the conductive member 106 forms the second electrode portion of the variable capacitance capacitor 100.
In the variable capacitance capacitor 100 formed as described above, as shown in FIG. 19B, in a state in which no pressure (pen pressure) is applied to the core body 101 (initial state), the conductive member 106 is physically separated from the second surface portion 103b of the dielectric 103, and is not in contact with the second surface portion 103b. When pressure is applied to the core body 101, the thickness of an air layer between the conductive member 106 and the second surface portion 103b of the dielectric 103 becomes smaller than in the initial state.
As the pressure applied to the core body 101 increases, the curved surface portion 106a of the conductive member 106 comes into contact with the second surface portion 103b of the dielectric 103. The contact area between the second surface portion 103b of the dielectric 103 and the curved surface portion 106a of the conductive member 106 corresponds to the pressure applied to the core body 101.
The state between the first electrode and the second electrode of the variable capacitance capacitor 100 changes as described above according to the pressing force applied to the core body 101. Thus, the capacitance of a capacitor formed between the first electrode and the second electrode changes according to the pressing force applied to the core body 101.
The above-described example is an example of a variable capacitance capacitor type pen pressure detecting module. Also in a case of an inductance detection type pen pressure detecting module, a plurality of parts are arranged in the axial direction of a core body of a position indicator (see Patent Document 2 (Japanese Patent Laid-Open No. 2002-244806), for example). In this case, the casing of the position indicator plays a role of a holder for housing the plurality of parts of the pen pressure detecting module.